Audio booster

The amplifier's gain is nominally 20 dB. Its frequency response is determined primarily by the value of just a few componentsâ€”primarily Cl and Rl. The values of the schematic diagram provide a response of Â±3.0 dB from about 120 Hz to better than 20,000 Hz. Actually, the frequency response is ruler flat from about 170 Hz to well over 20,000 Hz; it's the low end that deviates from a flat frequency response. The low end's roll-off is primarily a function of capacitor Cl (since Rl's resistive value is fixed). If Cl's value is changed to 0.1 pF, the low end's corner frequencyâ€”the frequency at which the low-end roll-off startsâ€”is reduced to about 70 Hz.

If you need an even deeper low-end roll-off, change Cl to a 1.0 ÂµÂ¥ capacitor; if it's an electrolytic type, make certain that it's installed into the circuit with the correct polarity, with the positive terminal connected to Ql's base terminal.